I have it on good authority that I stand to gain a 128gb ssd in the near future.
I'm sure you know what you're doing, but:
I'd strongly recommend a 500GB one if you can afford it. I tried going the 128 GB option and it didn't work out so well. I play skyrim, Starcraft 2, maybe a few small steam games and installed MS office. That's about all the drive had room for. There's overprovisioning which doesn't help either.
Drives can last many, many years if you're lucky.
I had originally bought a Samsung 840 Pro on sale as the 850 series was coming out. 128 GB wasn't enough, so holiday season, I bought a 480GB (Sandisk?) and reinstalled.
My 840 Pro went into my laptop for a while. It really helped when the laptop hit 3GB ram usage. The HDD used to freeze the laptop for 30+ seconds as it tried to write to the swap / pagefile. Also, SLC of the 840 Pro should have fair endurance even at 128GB capacity, so I'm not worried about using it as swap / pagefile.
Eventually, it became my root linux drive on my desktop and put /home onto a HDD (similar to having your documents folders on a HDD in windows) and will happily reside next to my other 4 drives I bought a 1TB HDD for data, later wanted a 2TB so I could back up the 1TB easily in case of drive failure. Then there's the DVD drive... I shouldn't buy any more drives XD I'm running out of both bays and ports.
Overall, I suggest buying more than what you think you need. My 95% full 16GB cell phone agrees
I started with a 32GB 4th gen iPod. Was way too much. Read everyone online saying go for at least 32 GB in a phone, but felt I'd be okay with a 16GB Andriod since 32 was too big on an iPod. I mean, it's manageable, but I don't have room for as much as I'd like and the Nexus 5X doesn't support SD cards